Ttyjfyk

Is there a standard (POSIX) way of asking the user some data from within a shell script, with read for example, while allowing live edition of the text being typed (what readline does)?

I know bash has read -e varname that allows for the person launching the script to use keyboard arrows for exemple, to edit or correct what has just been typed without deleting the last entered characters with backspace.

However, read -e is bash specific. And still, it is pretty cumbersome to delete all that has been wrote if you realise you made a mistake at the beginning of your long sentence...

The terminal driver does have line editing capabilities on most systems. You'll notice that you can use Backspace, Ctrl-U, sometimes Ctrl-W.

readline is a GNU library maintained alongside bash. There's nothing POSIX about it. POSIX defines an optional line editor (with vi key binding) for sh, but no provision to use it outside of sh.

The ksh93 shell uses that vi-style line editor (also supports emacs or gmacs-style) for its read builtin when both stdin and stderr are a terminal and the corresponding option has been set: set -o emacs; IFS= read -r var for instance for read to use an emacs-style line-editor.

POSIX does specify the vi editor though (optional), so you could invoke vi to edit the content of a temporary file.

The zsh equivalent of bash's read -e is vared (a lot more advanced as it's using zsh's zle (zsh line editor)).

In other shells, you can use some wrappers around readline or other line-editing libraries (like rlwrap), or you can invoke bash -c 'read -e...' or zsh -c 'vared...'.

What you could also do is give the opportunity to the user to launch an editor.

Like:

if ! IFS= read -r var; then
 if [ -n "$var" ]; then
 tmp=$(create_tempfile) # create_tempfile left as an exercise
 printf '%sn' "$var" > "$tmp"
 "$VISUAL:-$EDITOR:-vi" -- "$tmp"
 var=$(cat < "$tmp")
 rm -f -- "$tmp"
 else
 exit 1 # real EOF?
 fi
fi

Then the user can press Ctrl-D twice to launch an editor on what he has already entered.

Otherwise, I once wrote that function that should work on most terminals on most Unices that implements a simple line editor.

LE() od -vAn -to1); do
 while [ "$#" -gt 0 ]; do
 LE_k=$1
 shift
 if [ "$LE_k" = 033 ]; then
 case "$1$2$3" in
 133103*

To be used as:

LE 'Prompt: '

Or:

LE 'Prompt: [....]bbbbb' 4 . DEF

if you want a maximum length and/or different filling character and/or an initial value.